Physicochemical characteristics and source analysis of PM1 during winter haze-dust pollution event in Qingdao

During an episode of winter haze-dust pollution event in Qingdao from November 21 to December 2 in 2018, we continuously measured the mass concentration, chemical composition and number concentration of PM1, in combination with the routine monitoring data from a national ambient air quality station, to study pollutant characteristics, source attribution for this typical winter air pollution event. The results showed that the whole event could be divided into five stages: pre-haze (November 21 to 23), haze period (November 24 to 25), haze-dust mixing period (November 26), dust period (November 27 to 29), and post-dust period (November 30 to December 2). During the pollution, the mean mass concentration of PM1 was (40±20)µg/m3, and PM1 in the haze period was 2.03 times higher than that of the dust period. In the post-front, the dust air kept the air dry and was mainly dominated by cold dry dust particles, which were less affected by accumulated anthropogenic pollutants from the areas it passed through during the long distance transmission. During the pre-front, the air was mainly dominated by polluted air masses from regions with intense anthropogenic emissions, resulting in more than 12 hours delays between the peaks of PM2.5 and PM10 in the dust period. The mass concentrations of SO42- and NO3- in PM1during the haze period increased by 73% and 111% than those of the pre-haze, respectively. SOR and NOR during the haze period increased by 28% and 67% than those of the pre-haze, indicating that the secondary formation of NO3- increased significantly during the haze period. NH4+ in PM1 mainly existed in the form of (NH4)2SO4 and NH4NO3, when inorganic ions were sufficiently neutralized by ammonium. Before reaching Qingdao, air masses passed over of the regions with intense anthropogenic emissions, such as Shanxi, Hebei and northwest of Shandong. Thus, when the pre-front arrived, these anthropogenic pollutants leaded to 1.73 and 1.53 times increase of OC and EC masses in PM1 during the dust period than in the haze period. The mass proportion of SOC in total OC in the haze period was 0.43 lower than that that in the dust period (0.48). This indicated that the SOC formation during the haze period had been suppressed. © 2020, Editorial Board of China Environmental Science. All right reserved.